FI115506B - Method and apparatus for treating water - Google Patents

Description

115506

FIELD OF THE INVENTION

The invention relates to the production of highly purified water for special purposes. In particular, the invention relates to the production of purified water using a drop film evaporator and subsequent condensation.

BACKGROUND OF THE INVENTION For the purposes of this text, "purified water" generally means water that is purer than ordinary drinking water available from, e.g., a municipal water supply network. Highly purified water is required, for example, for a variety of medical purposes, such as the manufacture of drugs and the production of '' water for injections '', the quality of which is defined in official pharmacopoeias. Apparatus for producing such purified water may be of the so-called multi-stage distillation apparatus which utilizes a set of evaporative film evaporators 15. The evaporator of the falling film comprises a vertical group of evaporators which are located inside the heating mantle. The water supplied to the evaporator tubes at their upper end flows downwardly along the inner surface of the tubes, whereupon it evaporates and forms steam which is discharged from the lower end of the tube group together with non-evaporated water. In many devices designed to produce highly purified steam or water, the steam stream rotates 180 to 20 degrees and flows upward in an ascending space for this purpose, as the remaining water accumulates at the bottom of the device.

Upstream steam can, depending on the type of device, be exposed to different types of defroster • 1; purification treatments, whereby the separated droplets and impurities eventually converge to the aqueous phase • '· .. at the bottom of the evaporator, while the steam enters the heating mantle of the following evaporator:' ''. The aqueous phase becomes the feed water for the next stage and the steam condenses i · releasing heat, causing more steam to evaporate from the feed water and the cascade continues: - until the last evaporator is reached. The combined condensates from the heating mantles are cooled, respectively, condensed together with the vapor of the final stage; : 30 in the last heat exchanger to form a purified aqueous product.

• In this context, the reject stream is the stream of water that is permanently removed from the process. Generally, the stream is liquid water but may be a vapor-liquid mixture. Continuous process. in order to produce purified water by evaporation, removal of a sufficient amount of reject water »115506 to remove the separated impurities must be included. The ratio of reject water to product water is an important aspect of process efficiency. It follows from the substance balance that if the rejection current is insufficient, impurities will either accumulate in the equipment or be removed with the product, both of which are highly undesirable.

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Equipment for the production of purified water should be capable of continuous operation and capable of responding rapidly to fluctuations in consumption. Falling film hardware basically requires a certain time period to adjust to the growth in demand. As additional primary heat is supplied, it will take some time until the heat 10 has passed through the various steps and the resulting additional steam, which is then condensed into pure water. If the equipment is continuously operated at full capacity, purified water may need to be removed, which is inefficient in terms of energy consumption. If the system is stopped, the coolant will be consumed and the subsequent restart will consume energy. Finnish patent 79790 discloses a method and apparatus for reducing the required feed water by dividing water from the final stage of purified steam or water production plant into a reject stream and a recycle stream added to the feed water stream.

SUMMARY OF THE INVENTION A drop film evaporator apparatus for producing purified water may comprise a plurality of evaporation steps. Water is supplied to each stage, and water and steam are discharged at each '' stage. The heat contained in the steam leaving a certain stage is used in the next stage to further remove some of the water, whereupon the steam condenses. Combined condensed vapor phases, including separately the condensed vapor generated; >: 25 final step, form purified product water.

In accordance with the present invention, at least a portion of the product water is led to a circuit connected to the first inlet water inlet. The apparatus can thus be operated in a continuous recirculation mode, whereby the product water is returned as feed water to the beginning of the process. The entire system can thus operate in a state of continuity where only ': an amount of feed water enters the circulation sufficient to compensate for the reject current,'. and required to transport the separated impurities.

3 115506 This mode can be used eg during startup. When the product water is withdrawn for consumption along a product line which forks, a corresponding amount of feed water is allowed in. The control system ensures an adequate supply of primary heat as the load varies.

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Recycling also offers the opportunity to sanitize the supply and product departments. The water may be circulated through the inlet line, through the evaporation steps, and through the product heat exchanger at a temperature and for a period sufficient to ensure complete sterility.

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Brief Description of the Drawings

The invention will be explained in more detail below, with reference to the accompanying figure, which schematically shows the main components of the apparatus according to the invention.

IS Description of the Invention

Figure 1 shows an embodiment of a four-stage purified water production apparatus according to the invention. The feed water, preferably purified by filtration, ion exchange or other suitable methods, enters the inlet 1 through the inlet valve 2 into the feed cycle 3. After passing through the heat exchanger 4, the feed stream goes, through the transfer line 5, to the first as one of ordinary skill in the art will appreciate. Equipment vapor or other primary heat transfer medium (electrical heating may also be used) that comes from inlet 8, heats the casing side of evaporator portion 7 of the falling film. As the feed water flows as a film down the interior walls of the evaporation tubes (not shown), the water partially evaporates to vapor which is discharged; ',,, · from the bottom of the tubes together with the remaining water.

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The vapor is separated from the aqueous phase in the separating section 9 and led in line 10 to the jacket side of the next * · '···' evaporation step 11 and the aqueous phase forms the next evaporation step 11 I * Γ '30 feed water entering inlet 12. the step, preferably according to another pending patent application, or the prior art; *; only from the last step 14.

115506

Each stage produces steam and from the second stage 11 onwards to the final stage, the steam from the previous stage is condensed into product water while simultaneously providing more feed water evaporation. The temperature and pressure are at their maximum levels in the first stage, corresponding to the temperature of the first heat source 5 and decreasing towards the last stage. Between the steps there may be suitable throttling means 15. The steam from the last step is condensed in a recovery heat exchanger 4 where the combined condensates from the previous steps can also be cooled. The product water may be taken from outlet 17 or, in accordance with the invention, may enter the feed circuit 18, 3 for the purpose of recycling the process. Fresh feed water 10 is added at 1, the amount of feed water being equal to the sum of the product water removed and the reject stream. The amount of feed water can be controlled by a float valve.

In the illustrated embodiment, residual water from the final stage can also be introduced into the feed circuit via line 19. This is possible because in the illustrated embodiment 15, a rejection stream containing impurities is removed from each step; impurities do not become concentrated in the final residual water. The final residual water can also be discharged with the reject stream or partitioned into recirculation and reject stream (outlet 20) according to the prior art. The outlets (not shown) for the non-condensable soluble gases can be arranged, for example, at the tops of the evaporation portions.

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For sterilization purposes, the temperature of the feed cycle 18, 3, including the feed valve 2, ': may be raised to a sufficient level for a sufficient period of time using, for example, product water heat. The required duration and temperature will vary depending on the circumstances but will be readily determined by one of ordinary skill in the art.

25 .., - ,,. 1 At start-up, the water can be recirculated through the process using minimum, reject current and compensating supplement water. The operating temperature can be reached quickly and,: the equipment is sterilized thoroughly by allowing the temperature to rise to a sufficient * »'· 1 sterilization temperature in each part for a sufficient period of time.

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Claims (6)

5, 115506 A method of operating a multi-stage drop film evaporator apparatus for producing purified water, characterized in that at least a portion of the product water is returned to the inlet of the first 5-stage feed water. Method according to Claim 1, characterized in that all product water is returned to the inlet water of the first stage. Method according to claim 1 or 2, characterized in that at least a portion of the residual water of the last stage is returned to the inlet of the first stage feed water. An apparatus for producing purified water, the apparatus comprising a plurality of steps for producing steam 15 from the feed water, each step comprising a feed water inlet, a steam or heat transfer medium inlet, a steam outlet and a residual water outlet; and means for condensing said steam into product water, characterized in that the apparatus has a circulation for recirculating the product water to the first-stage inlet water inlet, said circulation comprising the inlet water inlet and the outlet of the product water. 20 Apparatus according to claim 4, characterized in that the residual water outlet of the last unit is connected in a circuit to the auxiliary inlet. 6, 115506